14.3- ADDITION POLYMERS Flashcards
What are polymers?
very large molecules built-up from small molecules called monomers
Examples of naturally occurring polymers? (4)
starch
proteins
cellulose
DNA
What was the first completely synthetic polymer?
Bakelite
When was Bakelite patented?
1907
What is one way of classifying polymers?
by the type of reaction by which they are made
What are addition polymers made from?
monomer(s) with a carbon-carbon double bond (alkenes)
The monomers that make up polymers are based on what?
ethene
What happens to the double bond in the monomer when it polymerises?
double bond opens and monomers bond together to form backbone of carbon atoms
What is phenylethane sometimes called?
styrene
What is poly(phenylethane) sometimes called?
polystyrene
What must addition polymers have?
backbone of carbon atoms
What must the monomers of addition polymers must contain?
at least two carbon atoms
Why must monomers of addition polymers must contain at least two carbon atoms?
so that there can be a carbon-carbon double bond
How can the properties of polymers materials be modified?
use of additives i.e. plasticisers
What are plasticisers?
small molecules than get between the polymer chains forcing them apart + allowing them to slide across each other
e.g. of plasticiser being used (before + after)
PVC rigid enough for use as drainpipes, with addition of plasticiser become flexible enough for making aprons
What is the backbone of a polyalkene?
long chain saturated alkane molecule
How are the bonds in alkanes described to be?
strong, non-polar C-C and C-H bonds
As the bond in alkenes are strong and non-polar, how reactive are they?
very unreactive molecules
As alkanes are very unreactive molecules, what cannot be done to them?
not attacked by biological agents, like enzymes
As alkanes cannot be attacked by biological agents, what are they described as?
not biodegradable
How is low density poly(ethene) made?
made by polymerising ethene at high pressure and high temperature via a free-radical mechanism
What does polymerising ethene at high pressure + high temperature via a free-radical mechanism produce?
polymer with a certain amount of chain branching
What is the chain branching in LDPE due to?
consequence of rather random nature of free-radical reactions
Are the branched chains in LDPE packed together?
not packed together particularly well
How flexible is LDPE?
quite flexible
How well does LDPE stretch?
stretches well
What is the density of LDPE like?
fairly low density
What does the properties of LDPE make it suitable for?
packaging (plastic bags), sheeting + insulation for electrical cables
At what conditions is high density polythene made?
temperatures + pressures little greater than room conditions + uses Ziegler-Natta catalyst
What does polymerising ethene at temperatures + pressures little greater than room conditions + use of Ziegler-Natta catalyst produce?
polymer with much less chain branching than LDPE
Can the chain pack together well? (HDPE)
yes
What is the density of HDPE like In comparison to LDPE?
greater
What is the melting temperature of HDPE like in comparison to LDPE?
higher
Typical uses of HDPE? (3)
milk crates
buckets
bottles
How can the amount of plastic be reduced?
by reusing or recycling it
What is the simplest form of recycling called?
mechanical recycling
What is the first step of mechanical recycling?
separate the different types of plastics
What is the second step of mechanical recycling?
plastics washed and once sorted they may be ground up into small pellets
What can happen to the small pellets of plastics in mechanical recycling?
be melted or remoulded
Example of mechanical recycling?
recycled soft drinks bottles made from PET used to make fleece clothes
What happens in feedstock recycling?
plastics heated to temperature that will break the polymer bonds + produce monomers
What can the monomers from feedstock recycling be used to do?
make new plastics
What type of plastic is poly(propene)? (feedstock recycling)
thermoplastic polymer
What happens to thermoplastic polymers when heated? (feedstock recycling)
soften so can be melted and re-used
Why can thermoplastics only be heated and re-used only be done a limited number of times?
as at each heating some of the chains break and become shorter so degrading the plastic’s properties
